ARAM FPS Issues

I'm having an issue at the moment with random FPS drops on ARAM. I've never suffered from this before and I would understand if it was only happening in teamfights etc. However I can go 15 minutes of an ARAM with 50+ FPS and then out of knowhere it'll drop to 7-12 FPS, then back up to 50ish. Then other ARAM's I spend nearly the whole game with less than 15 FPS. It's really annoying as I love playing ARAM and just wondered if anyone else had the same sort of problem? Or if there was any 'fix'?